A more uniform cladding thickness is retained on flat copper-clad steel wire by drawing the first rectangular sections, rather than rolling them, from round wire, and then rolling the final flat wire....http://www.google.com/patents/US3811311?utm_source=gb-gplus-sharePatent US3811311 - Making flat copper-clad steel wire

BACKGROUND OF THE INVENTION Copper-clad steel wire is known to combine the advantages of the high tensile strength of steel with the high electrical conductivity, and resistance to corrosion of copper. In spite of the fact that electroplating of copper has long been practical and economical for most purposes, for electrical conductors, it has been most advantageous to draw down a hot-rolled casting of a copper ingot around a steel core. This is due to the superior bonding of the copper and'steel in such a structure and to the fact that the economy of electroplating is lessened for greater wall thickness of copper. Copper-clad steel wire has been standardized by conductivity in American Society for Testing Materials (ASTM) Standard Specificaton B 22 7-70. This standard requires that the thickness of copper cladding of grade .40 HS shall be no less than 12 mils on a wire 0.2 to 0.21 inch in diameter. The thickness of cladding of an 0.09 inch wire is required to be no less than mils. It should be noted that the expression copper-clad steel as used by ASTM, and in this application, is not limited to the cast ingot method of forming the clad product, and other methods, such as high current density plating and hot swaging have been known.

To make square copper-clad steel wire it has been usual to cold-roll the standard round wire. However, where it is desired to obtain flat copper-clad wire, such as wire having the long dimension of its section at least four times the short dimension, it is found that cold rolling preferentially rolls the copper to the edges and leaves inadequate protection on the flats.

SUMMARY We have discovered that a flat copper-clad steel wire can be made with good distribution of the copper over BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a section of prior art rolled flat wire. FIG. 2 shows a series of wire sections of flat wire formed in the steps of our method.

FIG. 3 shows the steps in the method of our invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT FIG. I represents prior art efforts to roll copper-clad steel flat, the flat section 11 with a steel core 12 and copper cladding 13 having been rolled in a series of passes from a round copper-clad steel wire such as the wire 14 (FIG. 2). Rolling has had the effect of pushing a disproportionate amount of the copper to the edges 16, 17 and of leaving an irregular cladding with thin spots, such as 18, on the surface having the longer dimension. Examples 1, 2.and 3 below illustrate the results of rolling copper-clad steel wire, of grade 40 HS ASTM B 227-70.

When, instead of being rolled, the round wire 14 was drawn through a series'of wire drawing dies 19, 20, 21, 22, 23 (FIG. 3) to the respective sections 24, 25, 26, 27, 28 and was only then rolled, in a single pass, to a section 29, it was found to have the improved cladding distribution of EXAMPLE 4. In this case the thickness of cladding was about 18 mils, 6.25 percent of the wire diameter.

Minimum copper on flats. mils If, instead of drawing in a single pass, the wire is taken up after each die passage, a wide choice of reduction ratios may be made but the cost of the drawing operation will be increased prohibitively for most commercial purposes, although still falling within the scope of our invention.

Starting with a 0.286 inch diameter wire having an area of section of 0.0642 square inches, we have found it advantageous to select the dies 19, 20, 21, 22, 23 to provide respective sectional areas of 0.0475, 0.036, 0.02765, 0.02135, and 0.01667 square inches, the final section, 28 from the die 23 being 0.090 X 0.205 inch. After rolling to 0.050 X 0.245 inch the section 29, which retains rounded corners, has an area somewhat less than 0.01225 square inch. In this embodiment the ratio of the long dimension to the short dimension of the section 28, i.e., the width to the thickness, is 2.28 to 1 and the ratio for the rolled section 29 is 4.9 to 1. The minimum thickness of cladding of the flat section made in EXAMPLE 4 is seen to be 5.6 mils which is over 10 percent of the thickness of the flat section. Where a precise control of the width of the section 29 is required the flat wire is passed through edge rolls which merely flatten the curvature of the copper on the edges, but do not affect the steel. Such edge rolling, which accounts for some squaring of the edges of the flat section 29 of FIG. 3 is not an element of the novelty of the present invention.

Wehave invented a new and useful method of which the foregoing description has been exemplary rather than definitive, and for which we desire an award of 3. The method of claim 2 wherein the longer dimension of said'rectangular section after drawing but prior to rolling is at least twice the shorter dimension of said section.

4. The method of claim 1 wherein said cold drawing into a rectangular section is effected through a plurality of dies in a continuous run.

5. The method of claim 3 wherein said cold drawing into a rectangular section is effected through a plurality of dies in a continuous run,

6. The method of claim 2 wherein said longer dimension exceeds the longer dimension of the final of said rectangular sections after drawing but prior to rolling. =l